Sedimentology is the study of sedimentary rocks that are generally formed by: the deposition of rock fragments which have been transported from their source to another location by water or air (sandstone and shale), precipitation from a liquid or solution (salt, gypsum), and remains (shells, skeletons and organic matter) of organisms (limestone, coal). Sedimentary rocks are deposited in layers known as strata. Stratigraphy is the study of the origin, composition, distribution and succession of these strata. Modeling programs, particularly forward stratigraphic modeling programs, may assist the study of the stratigraphy of a particular area by creating a model of a particular basin that may be used to more closely study the basin than would be possible and/or economically feasible using solely direct measurements of the characteristics of the basin.
Oil and gas reservoirs as well as groundwater resources occur in sedimentary basins filled with strata of diverse compositions that contain fluids (water, oil, gas) in variable proportions and spatial distributions. The distribution of fluids is strongly controlled by petrophysical (e.g., porosity and permeability) and geometric (e.g., continuity and connectivity) properties of strata.
To recover petroleum from these reservoirs typically requires drilling through thousands of feet of overlying rock. The drilling of oil and gas wells is typically a very expensive endeavor. Accordingly, before incurring such a large expense, those involved in the exploration and production of oil and gas reservoirs normally seek to obtain an understanding of the basin geology and, in particular, the basin sedimentology and stratigraphy so that an oil/gas well is drilled in a location that is likely to achieve the desired result. In the case of oil and gas exploration, geologic and seismic data are used to predict the location of sedimentary rocks and structures that are likely to contain an oil/gas reservoir. With respect to developing an oil/gas reservoir, geologic and seismic data are used to predict locations for drilling wells that will facilitate the extraction of additional oil from a reservoir.
Currently, there are many different techniques available for obtaining sedimentologic and stratigraphic data. One technique is seismic surveying, which involves: transmitting sound waves from the surface into the earth, recording the waves that are reflected back to the surface when the transmitted wave encounters interfaces between strata, fractures and the like in the underlying earth, and analyzing the reflected signals to make geological inferences about sedimentary rocks and fluids encountered by the waves as they propagate through the earth. Other techniques that are also used are coring and well logging, which involve taking samples of the various rocks and fluids encountered as a well is drilled, noting the extent of each particular kind of rock that is encountered during the drilling, and inserting various instruments into the well that measure various rock and fluid properties, such as porosity. These techniques obtain direct and indirect information only at the coring or well sites. Most of the techniques for obtaining sedimentologic and sedimentary data are relatively expensive and are limited to the locations in which the data are taken, i.e., the data obtained by one of these techniques at a particular location are not representative of the underlying geology for more than a short distance away from the location at which the data were taken. As a consequence, any conclusions drawn with respect to sedimentological and sedimentary attributes are subject to increasing uncertainty as the location of interest becomes increasingly remote from the locations at which the data are taken. However, even when only sparse (i.e., potentially uncertain) direct data on a location is available, those involved may wish to obtain some type of additional reassurance that extractable material is available in a location before investing in expensive additional testing and/or drilling procedures for a particular location.